Method for producing foamed plastic insulator

Abstract

A foamed plastic insulator such as an insulated wire having a foamed plastic material insulation layer formed over a conductor. The plastic material includes at least one component having a swelling ratio greater than 55%, and the component comprises at least 20% by weight of the insulation layer. The insulated wire is produced by adding a blowing agent such as a chemical blowing agent and an inert gas and extruding the mixture over a conductor.

We claim: 
     
       1. A method for producing a foamed plastic insulator comprising the steps of: preparing a plastic material comprising low density polyethylene having a melt flow swelling ratio of at least 55%   adding a chemical and/or inert gas blowing agent to said plastic material,   extruding a mixture of said plastic material and said blowing agent over a conductor, and   foaming said mixture to produce foamed insulation layer.   
     
     
       2. The method of claim 1 further comprising the step of extruding a second plastic material over said mixture simultaneously with the extrusion of said mixture to form a solid layer. 
     
     
       3. The method of claim 1 wherein said blowing agent is a chemical blowing agent selected from the group consisting of azodicarbonamide, 4,4'-oxybis(bensenesulfonylhydrazide). 
     
     
       4. The method of claim 3, wherein said mixture of at least two kinds of polyolefins consists essentially of at least 20 weight percent of low density polyethylene whose melt flow swelling ratio is greater than 55%. 
     
     
       5. The method of claim 2, wherein said solid layer is polyolefin. 
     
     
       6. The method of claim 1 wherein said blowing agent is a chemical blowing agent selected from the group consisting of azodicarbonamide, 4,4'-oxybis(bensenesulfonylhydrazide). 
     
     
       7. The method of claim 1 wherein said blowing agent is an inert gas blowing agent selected from the group consisting of nitrogen, argon, and carbonic acid gases.